In an image forming apparatus, an electrostatic latent image is formed on a surface of a photosensitive drum. A toner is supplied to the electrostatic latent image from a developing device, so that the electrostatic latent image is visualized in a toner image, whereby the toner image is carried on the surface of the photosensitive drum. Then, the toner image is transferred onto a sheet, resulting in achievement of image formation onto the sheet.
The developing device includes a casing having an opening that is opened toward the photosensitive drum, a developing roller that carries a toner accommodated in the casing, and a layer-thickness regulating blade for regulating a layer thickness of the toner carried on the developing roller. The developing roller is rotatably supported at the opening of the casing with a portion of the surface thereof exposed. The layer-thickness regulating blade is extended along the axial direction of the developing roller, and a pressing portion having a semicircular section provided at the distal-end portion thereof is in pressure contact with the surface of the developing roller.
The toner in the casing is supplied onto the surface of the developing roller, and then passes through between the pressing portion of the layer-thickness regulating blade and the surface of the developing roller, along with the rotation of the developing roller. This passage allows the toner to be carried on the surface of the developing roller while forming a thin layer having a uniform thickness. The toner thus carried on the surface of the developing roller is supplied to the electrostatic latent image formed on the surface of the photosensitive drum when coming in contact with the surface of the photosensitive drum.
The layer-thickness regulating blade includes a support member attached to the casing, and a leaf-spring member extended toward the developing roller from the support member. The pressing portion is provided at the tip end portion (distal-end portion) of the leaf-spring member.
The support member includes a back support member, and a front support member arranged in opposed relation thereto. The support member is fixed to the casing with a screw that penetrates the front support member, the leaf-spring member, and the back support member while sandwiching the proximal edge of the leaf-spring member (end portion of the side opposite to a side where the pressing portion is provided) between the back support member and the front support member.
However, when both end portions of the support member in the longitudinal direction are fixed to the casing with the screws, the center portion of the support member in the longitudinal direction may bend in a direction in which the pressing portion is spaced away from the surface of the developing roller. Thus, when the support member bends, the leaf-spring member also bends. Therefore, the pressing portion cannot be uniformly brought into pressure contact with the developing roller in its axial direction. As a result, the layer thickness of the toner carried on the surface of the developing roller is not uniform, thereby generating streaks in the image formed on a sheet due to undesired density unevenness.
When a local force acts on a portion in which the screw penetrates the leaf-spring member, there is a possibility that the leaf-spring member may be deformed so as to be waved. When such deformation arises, the pressing portion cannot be uniformly brought into pressure contact with the developing roller in its axial direction.
To cope with this problem, there has been proposed that a developing-agent restricting member equivalent to the leaf-spring member is fixed to the support member by adhesion. However, with the proposed arrangement, dust or the like adheres to an adhesive layer between the developing-agent restricting member and the support member. A small image forming apparatus such as a laser printer cannot define a sufficient space between the optical path of laser light which is irradiated to a surface of a photosensitive drum from the exposure device and a support member. Therefore, when dust or the like adheres to the adhesive layer, the adhered dust or the like lies on the optical path of laser light. This interrupts the optical path, thereby producing streaks (white streaks) in the image formed on a sheet due to exposure failure.